There is a recent advancement of use of computer networks and smart phones for various services, e.g., music, social networks, games, etc. As a network of users that are linked via the computer networks and smart phones increases, there is an increased user interest in involving other users. For example, a user would like to invite his or her friend to play a game, to listen to music, etc. With an increase in a number of users, it is difficult for the user to keep up with various operations that are associated with the invitations.